Method of ofdm transmission in a millimetre-wave wland and corresponding system

ABSTRACT

A method of managing an OFDM transmission system, for instance a millimetre-wave WLAN, wherein a plurality of sets of samples including at least one set (X 1 , X 2 , . . . X N ) of generally non-zero samples is subject to an integral transform transmitted in the integral-transformed format and subject to a complementary integral transform to reconstruct the at least one set of generally non-zero samples. The method includes the step of assigning non-overlapping sets of samples to a plurality of terminals.

FIELD OF THE INVENTION

The present invention relates to transmission systems based on theoperating scheme usually referred to as OFDM (Orthogonal FrequencyDomain Multiplex) and was developed by paying specific attention to thepossible application to wireless local area networks (currently referredto as W-LANs or WLANs) such as millimetre-wave WLAN systems. Referenceto this preferred field of application is not to be construed asintended to limit the scope of applicability of the invention: in factthe invention can be advantageously applied to other carriers than amillimetre-wave carrier and to communication systems other than a WLAN.

DESCRIPTION OF THE RELATED ART

In an OFDM transmission system, a set of non-zero samples (informationsamples) is subject to an integral transform (such as an Inverse FastFourier Transform or IFFT), transmitted in such an integral-transformedformat and subject to a complementary integral transform (such as a FFT)to reconstruct the non-zero samples transmitted.

Current WLAN standards such as IEEE 802.11a and IEEE 802.11b provide forall the stations located in a certain access area being connected bysharing only one channel at a time. This represents a strong limitationin view of the requests for an ever-increasing bandwidth being madeavailable for broadband services such as video streaming and fastInternet access.

This fact is acknowledged e.g. in “The AC006 MEDIAN Project-Overview andthe State of the Art” by C. Ciotti and J. Borowski, SummitGranada-SPAIN, November 1996, available with the Institute for Mobileand Satellite Communications (IMST) of Kamp-Lintfort, Germany.

One of the main objectives of the MEDIAN Project is the development andstandardization of high-speed wireless costumer premises local areanetwork for multimedia applications in the 60 GHz range (with a net datarate up to 150 Mbit/s) connected to the fixed Asynchronous Transfer Mode(ATM) network. The MEDIAN system architecture uses an orthogonalfrequency domain multiplex (OFDM) modulation scheme characterized by 512sub-carriers.

As in existing standards, in the arrangement according to the MEDIANProject, only a single channel (200 MHz) is used to implement a WLANnetwork, and such a channel corresponds to the set of non-zero samplesabove described.

Consequently, multiple receiver/transmitter modules, each using adistinct band (i.e. a distinct OFDM transmission system each using adistinct band), are required in order to operate over a largertransmission band.

Such prior art arrangements fail to recognize that the use ofmillimetre-wave carriers (e.g. in the range between 40-60 GHz) makes itpossible to allocate to the users a much larger frequency band (forinstance 4-5 GHz) in comparison with existing WLAN systems as describedin the standards such as IEEE 802.11a e IEEE 802.11b.

OBJECTS AND SUMMARY OF THE PRESENT INVENTION

The object of the present invention is thus to provide an improvedarrangement taking advantage of the availability of a larger frequencyband to be allocated around millimetre-wave carriers orsub-millimetre-wave carriers used in WLAN networks.

According to the present invention, such an object is achieved by meansof a method having the features set forth in the claims that follow. Thepresent invention also relates to a corresponding system, to terminalsfor use in such a system, as well as corresponding computer programproducts directly loadable into the memory of a computer and includingsoftware code portions performing the method of the invention and/orimplementing a terminal for use in the network according to theinvention when the product is run on a computer.

A preferred embodiment of the invention is thus a method of managing oneOFDM transmission system, wherein a plurality of sets of samplesincluding at least one set (X₁, X₂, . . . X_(N)) of a generally non-zerosamples is subject to an integral transform, transmitted in theintegral-transformed format and subject to a complementary integraltransform to reconstruct the set of generally non-zero samples.

The preferred method provides the steps of including in said system aplurality of terminals (i.e. stations), assigning to these terminalsrespective non-overlapping sets of samples or positions within saidplurality of sets of samples, and transmitting the samples pertaining toeach terminal by inserting the non-zero samples to be transmitted (X₁,X₂, . . . X_(N)) in the respective positions assigned to the terminal.

Preferably, the system includes at least one further terminal intendedto operate as an access point and adapted for exchanging samples withsaid plurality of terminals. The further terminal subjects to at leastone of the integral transform or the complementary integral transform aplurality of sets of samples including at least two non-overlapping setsof non-zero samples pertaining to two respective different terminals ofsaid plurality.

The integral transform is preferably selected from the group consistingof the Fast Fourier Transform (FFT) and the Inverse Fast FourierTransform (IFFT).

In particular, the arrangement described herein takes advantage of thefrequency band available to the users of a millimetre-wave WLAN networkor sub-millimetre-wave WLAN network by causing a plurality of stationslocated in a given area to use, simultaneously, a correspondingplurality of channels.

This is contrary to existing WLAN standards, which refer to only onechannel being used at a time for each access area.

The invention can be used, moreover, with frequency band in the range ofstandard WLAN, by scaling, accordingly, the carrier and thecorresponding band.

The arrangement described herein is based on the recognition of the factthat the OFDM coding scheme carries within itself the criterion oforthogonality of the symbols transmitted.

The arrangement described herein implements, in particular, an efficientmultiplex system and an improved interface for a millimetre-wavetransmitter/receiver module, exploiting the inherent broadbandcharacteristics of a millimetre-wave carrier.

The arrangement described herein complies in an efficient and flexibleway with the demand for growing wide bands, while using only onemillimetre-wave module to manage the plurality of independent channelsat the same time. Management of multiple stations is performeddigitally.

BRIEF DESCRIPTION OF THE ANNEXED DRAWINGS

The invention will now be described, by way of example only, byreferring to the enclosed figures of drawing, wherein:

FIG. 1 is a block diagram representing a typical WLAN networkarchitecture,

FIG. 2 schematically represents a millimetre-wave transmitter/receiverstation (transceiver),

FIG. 3 details a millimetre-wave WLAN net interface,

FIG. 4 is a block diagram portraying millimetre-WLAN channel managementin a local station, and

FIG. 5 is a block diagram portraying millimetre-WLAN channel managementin an access point.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 depicts a typical example of millimetre-wave WLAN (mm-WLAN)network architecture.

In the diagram of FIG. 1, reference numerals 14 indicates respectiveterminals such as PCs, mobile phones, and so on each provided with arespective mm-WLAN card intended to permit communication with arespective access point 13 serving a corresponding access area 12.

Communication with other access areas 12 is via a distribution system DScomprised e.g. of Gbit Ethernet or fibre optic network. The distributionsystem DS connects the various access points 13 serving the access areas12. A server 10 and a gateway 11 are usually provided in order to permitaccess to shared databases (through the server 10) or to externalnetworks such as the Internet (through the gateway 11).

The diagram of FIG. 2 details the architecture of a transmitter/receivermillimetre-wave WLAN station. This applies in a substantially identicalmanner to the various stations 14 with millimetre-wave card shown inFIG. 1 and to the access points 13 as well.

Essentially, the architecture of FIG. 2 is comprised of three basicelements, namely:

-   -   a millimetre-wave transceiver 20 provided with an antenna 20 a,    -   a net-WLAN module 21 usually mounted jointly with the        transceiver 20 on a millimetre-WLAN card 23, and    -   a processor unit 22 which, in the case of the stations 14, may        be e.g. a personal computer or portable telephone or another        type of terminal.

The elements 20 and 21 including the antenna 20 a for the transceiver 20are preferably mounted on the card 23 in a configuration adapted topermit insertion into the input/output module 22, for instance by PCIbus.

The millimetre-wave transceiver module 20 can be of the type describedin the article by Y. Mimino et al., “A 60 GHz Millimeter-wave MMICChipset for Broadband Wireless Access System Front-end”-2002 IEEE MTT-S.Digest TH3A-2 or in the article by K. Fujii et al., “60 GHz-MMIC Chipsetfor l-Gbit/s Wireless Links”-2002 IEEE MTT-S. Digest TH3A-3.

As better detailed in FIG. 3, the module 21 includes high-frequencyanalogue-to-digital and digital-to-analogue converters 33 and 34,respectively. These are connected to a serial-to-parallel converter 35(for instance a shift register), a millimetre-WLAN general managementunit 36 (to be described in greater detail in the following) and amedium access control (MAC) unit 37.

Advantageously, the converters 33 and 34 are of the type currentlyavailable as HYPRES, Inc. cryogenic devices or are based on 0.13 micronCMOS technology.

As indicated, the description provided in the foregoing applies both tothe stations 14 and the access points 13.

In case of access point 13, the processor module 22 may be e.g. acontrol unit adapted, in a known way, to manage traffic control betweenthe stations 14.

However, the MAC 37 included in the net WLAN module 21 is more complexin the case of the access points 13 than in the case of the stations 14.Also, in the case of the access points 13 the MAC unit 37 is generallyrequired to operate at higher speeds, which is compatible with currenttechnologies such as Gigabit-Ethernet switch technology currentlyavailable with CISCO SYSTEMS, Inc.

Architecture and operation of the channel management units 36 issubstantially similar in the case of the local stations (FIG. 4) and inthe case of the access points 13 (FIG. 5).

Each local station module 23 is essentially required to manage dataflows from and to the respective processor unit or terminal 22.Conversely, each access point 13 will simultaneously manage data flowsto and from all the stations 14 located in the area 12 served by theaccess point in question.

An orthogonal frequency domain multiplex (OFDM) scheme is essentiallybased on the joint use of an integral transform (such as a Fast FourierTransform or FFT) and the complementary inverse transform (such as theInverse Fast Fourier Transform or IFFT).

Both FIGS. 4 and 5 refer to the use of FFT in reception and the use ofIFFT in transmission which is the conventional representation of OFDM.Those of skill in the art will however appreciate that any type ofintegral transform admitting a complementary inverse transform can beused for implementing an OFDM scheme.

The IFFT transmission modules 41 and FFT reception modules 42 shown inFIGS. 4 and 5 carry out orthogonal frequency division multiplexing(OFDM) operations.

The modules in question can be advantageously constituted by Fast MathProcessors available with Intrinsity, Inc.

In both FIGS. 4 and 5, reference 43 designates buffer unit that managesthe input and output samples by converting them from parallel to serialform and vice versa. The buffer unit 43 is typically comprised of ashift register.

Reference numerals 38 and 37 designate a logical link control (LLC)block and the MAC block, respectively.

The LLC block 38 is typically a module referred to the upper part of thesecond level of the standard open system interconnection (OSI) model.Essentially, the module 38 and the MAC module 37 together represent thedata link layer of the OSI model and perform the driver functionalitiesfor the millimetre-wave card.

Both in the local stations 14 and in the access points 13 the MAC levelis implemented on the network card 23, while the logical link controllayer is typically comprised of a software module contained in theprocessor unit 22.

Operation of the system just described is based on a time divisionduplex (TDD) pattern, wherein the transmission and reception phases areallotted respective time slots. Hardware components such as buffers andserial-to-parallel converters can thus be re-used both in transmissionand in reception.

Essentially, the transceiver module 20 receives via its antenna 20 a thewireless signal and delivers it to the net-WLAN module 21. There thesignal is processed and converted to a form compatible with the upperlevels of the OSI model (essentially, the LLC and the TCP/IP levels inthe processor unit 22).

In a symmetrical way, the processor unit 22 delivers its output signalsto the net-WLAN module 21, which converts such signals to a transmissionformat adapted to the transceiver module 20.

More specifically, signals from the millimetre-wave transceiver module20 are processed by the analogue-to-digital converter 33 and convertedinto the parallel form in the serial-to-parallel converter 35. Thecorresponding samples are then processed in the channel management block36. The output samples from the block 36 are then delivered to the MAClevel 38 for their final destination to the processor unit 22.

The signals being transmitted follow exactly the same path in theopposite direction (in different time slots for a TDD operation mode)and are sent to the transceiver module 20 through thedigital-to-analogue converter 34.

Considering first the data output from a local station (FIG. 4), thedata to be transmitted are grouped in M sets of N samples and sent intothe buffer 43 including locations for N×M samples.

In fact, out of the N×M positions available in the buffer 43, only Npositions are reserved for samples conveying a signal. These samplesconveying the signal to be transmitted are currently referred to brieflyas “non-zero” samples, even though—strictly speaking—they may possiblyinclude one or more samples corresponding to a zero-level signal.

In conventional OFDM transmission, the N non-zero samples are usuallyallotted—the same—position within the buffer 43. Typically, thisposition corresponds to the first N positions within the buffer.

In conventional OFDM systems, this applies to all local stations 14.Consequently, transmission of data from the various local stations 14(and, similarly, transmission of signals towards the various localstation 14) must be staggered over time by causing transmission from orto each single local station to take place within a given time interval.

As opposed thereto, the arrangement described herein essentiallyconsiders the N×M positions available in the buffer 43 as representing Mchannels each adapted for transmitting N samples.

Consequently, in the arrangement described herein, a given local station(hereinafter “station 1”) will place its N non-zero samples X₁ X₂ . . ., X_(N) to be transmitted at a given instant of time in the first Npositions of the buffer 43, such first N positions representing a firstchannel in the OFDM scheme of the arrangement shown herein.

Another station (hereinafter “station 2”), will place its set of Nnon-zero samples to be transmitted at the same instant of time in thepositions X_(N+1) to X_(2N) in the buffer 43, these N positions, beingnon-overlapping with the positions X₁ to X_(N) allotted to “station 1”,representing a second channel in the system.

Proceeding similarly for all the other stations in the system, a M-thlocal station will finally place a respective set of N samples to betransmitted at the same instant of time in the positions X_(N×(M−1)+1)and X_(N×M) of the buffer 43, these N positions, being non-overlappingwith the positions X₁ to X_(N) allotted to “station 1”, the positionsX_(N+1) to X_(2N) allotted to “station 2” and so on, representing a M-thchannel in the system.

Stated otherwise, each local station 14 will include in the respectivechannel management module 36 a buffer such as buffer 43, with theproviso that the i-th local station 14 will be allotted the i-th channelwithin the OFDM transmission scheme, such a channel being in factrepresented by a respective set of N positions assigned (in anon-overlapping manner with those sets allotted to other stations) inthe buffer 43.

The i-th local station in question will put its N non-zero samples to betransmitted at a given time at those N positions of the buffer 43representing the channel allotted to that station, while all the otherpositions in the buffer 43 will be forcibly set to zero.

The N×M sample sets thus created (including N non-zero samples andN×(M−1) samples forced to zero) will then be processed according to thestandard OFDM processing procedure by subjecting it to the Inverse FastFourier Transform IFFT in the module 41 to be then serialized in themodule 35 and transmitted to the digital-to-analogue converter 34.

The output signal thus generated will then be used to modulate themillimetre-wave module 20 and then transferred to the antenna 20 a forwireless transmission within the WLAN.

The samples associated with a channel of interest will thus be definedin the frequency domain (like in prior-art OFDM systems) and separatedin the buffer 43 by selecting the correct channel allotted in anon-overlapping manner to a given local station, this operation beingeasily accomplished by the MAC module 38.

After IFFT processing, in view of the spectrum separation, theinformation transmitted in respect of each and every channel defined inthe buffer 43 will not be affected by interference with the informationtransmitted from other local stations by using other channels, namelyother groups of samples within the respective buffers 43.

The signals so transmitted (during the same time interval) by thevarious local stations 14 will be received at the access point 13serving the respective local area.

After reception in the module 20, the signal will be subject toanalogue-to-digital conversion in the module 33 and then re-arrangedfrom the serial to the parallel format in the module 35 to be subject toFast Fourier Processing in the module 42.

As a result of this, the input samples will be reconverted to thefrequency domain and, because of their definition, will be loaded in thebuffer 43 of the access point 13 in distinct, non-overlapping sectionsof the buffer 43. The buffer 43 in the access point 13 will include Msuch sections, each adapted to correspond to a given transmissionchannel.

Each channel will in turn include N samples pertaining to transmissiontoward the access point 13 from a given local station 14 withoutinterference.

Information achieved in the reception phase is delivered to the upperlevels of the corresponding OSI model, namely the MAC module 37 and theLLC module 38.

Of course, the access point acting as a receiver will have to match theincoming samples associated with the various transmitting stations withoutput buffer intervals corresponding to the channel of destination,namely the local station transmitting the respective signal. Aninterface module 44 interposed between the buffer 43 and the MAC and LLCmodules 37 and 38 easily achieves such a task.

Transmission from the access point 13 to the various local stations 14will take place according to the same criteria described in theforegoing.

The samples to be transmitted to the various local stations (forinstance, M sets of N samples each) will be loaded via the interface 44into the buffer 43 by arranging the N samples intended to be transmittedto “station 1” in the first N positions of the buffer 43, the N samplesintended to be transmitted to “station 2” in the positions N+1 to N ofthe same buffer, and so on proceeding for the remaining stations in anon-overlapping manner.

After transmission (taking place within the same interval for allstations 14) OFDM processing as described in the foregoing will leadeach local station 14 to have its buffer 43 (acting as a receptionbuffer) filled with N generally non-zero samples located in thepositions corresponding to the channel assigned to that station.

Operation as described permits communication from the various localstations 14 to the access point 13 and from the access point 13 to thevarious local stations 14 to take place simultaneously (namely withoutany need of staggering transmission to and from separate stations overdifferent time intervals), the only requirement being that propersynchronization is ensured when transmitting the blocks of N×M samples.This result can be achieved by known means, e.g. by resorting to aso-called “beacon” signal.

In a millimetre-wave WLAN system with a 4 GHz bandwidth between 58 and62 GHz, a preferred choice of the system parameters is as follows:

-   -   4 GHz band around a 60 GHz carrier;    -   M=16 number of channels/stations, that may simultaneously        transmit in an area covered by an access point;    -   N=64 number of sub-carriers in one single channel (the OFDM        features of multipath rejection, strictly depending on this        parameter, are therefore maintained;    -   64×16=1.024 number of overall samples in the FFT/IFFT modules;    -   250 MHz: band available for each channel;    -   150 Mbit/s, minimum bit rate achievable for each station.

It will be appreciated that the arrangement just disclosed combined theadvantages of traditional OFDM techniques (effectively combatingmultipath propagation effects, fast fading in free-space propagation andfrequency-selective channels) with the simplicity of digital frequencymultiplexing.

Additionally, local oscillators and mixers are not required formodulating the channels as channel selection is achieved spatially, byselecting the right interval of samples. This affords a greatflexibility in band allocation and association with different localstations. Thanks to contiguous positioning of the transmission samples,two or more channels can be joined to form a “wider” channel, whichleads to increased additional resources.

Multiplexing can be managed completely at the software level, withincreased flexibility towards upper levels of the reference OSI model,which leads a simplification of the interface between the physical leveland the data link-MAC.

Division of information and its allocation to the right channel ismanaged in a completely digital manner by using FFT and IFFT for channelselection. Additionally, the OFDM multiplexing function is integratedwith the FFT and IFFT signal processing, while the interval of samplesallotted to each station is dynamically selected at the MAC level.

Modularity in the multiplexing structure can be achieved with thepossibility of joining channels without changing the systemarchitecture. The MAC level identifies each single channel with a valueused to detecting the buffering sample interval. This allows dynamicselection of the channel of interest operated by the MAC level such aresult being obtained simply with the selection of a specific group ofreceived samples.

Although the described example relates to a millimetre wave WLAN, theinvention equally applies to other types of network, for examplesub-millimetre wave WLAN, WLAN using other frequency bands or, ingeneral, digital local area networks.

Of course, without prejudice to the underlined principle of theinvention, the details and embodiment may vary, even significantly, withrespect to what has been described and shown, without departing from thescope of the invention as defined by the annexed claims.

1-22. (canceled)
 23. A method of managing a transmission system whereina plurality of sets of samples (N×M) is subject to an integral transformtransmitted in said integral-transformed format and subject to acomplementary integral transform to reconstruct said plurality of set ofsamples (N×M), comprising the steps of: including in said system aplurality of terminals; assigning to said terminals respectivenon-overlapping sets of samples or positions within said plurality ofsets of samples; and transmitting a set (X₁, X₂, . . . X_(N)) ofnon-zero samples pertaining to a first terminal of said plurality byinserting said samples in the respective position assigned to said firstterminal.
 24. The method of claim 23, further comprising the steps of:including in said system at least one further terminal adapted forexchanging samples with said plurality of terminals; causing said atleast one further terminal to subject to at least one of said integraltransform and said complementary integral transform a plurality of setsof samples including at least two non-overlapping sets of non-zerosamples, said two non-overlapping sets of samples pertaining to tworespective different terminals of said plurality.
 25. The method ofclaim 23, wherein said integral transform is selected from the group ofthe Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform(IFFT).
 26. The method of claim 23, further comprising the steps oftransmitting said samples in said integral transformed format over amillimetre-wave carrier.
 27. The method of claim 26, wherein saidmillimetre-wave carrier is selected in the frequency range of 60 GHz.28. A transmission system comprising: an integral transform module forsubjecting a plurality of sets of samples including at least one set(X₁, X₂, . . . X_(N)) of a non-zero sample to an integral transform; atransmitter for transmitting assigned non-overlapping sets comprising atleast one set (X₁, X₂, . . . X_(N)) of samples in saidintegral-transformed format; a receiver for receiving said sets ofsamples transmitted in said integral-transformed format; and acomplementary integral transform module for subjecting said samplestransmitted in said integral-transformed format as received by saidreceiver to a complementary integral transform and reconstructingtherefrom said at least one set of non-zero samples.
 29. The system ofclaim 28, wherein at least one terminal having assigned anon-overlapping set of samples or position within said plurality of setsof samples and comprising at least one of: said integral transformmodule and said transmitter; or said receiver and said complementaryintegral transform module.
 30. The system of claim 28, furthercomprising at least one further terminal adapted for exchanging sampleswith said plurality of terminals, said at least one further terminalincluding at least one of said integral transform module andcomplementary integral transform module for subjecting to at least oneof said integral transform and said complementary integral transformsets of samples including at least two non-overlapping sets of non-zerosamples, non-overlapping sets of samples pertaining to two respectivedifferent terminals of said plurality.
 31. The system of claim 30, inthe form of a WLAN network, wherein at least one further terminal is anaccess point of said WLAN network.
 32. The system of claim 28, whereinat least one of a transmitter and receiver operates over amillimetre-wave carrier.
 33. The system of claim 32, wherein at leastone of a transmitter and receiver operates over a carrier in thefrequency range of 60 GHz.
 34. A transmitter terminal for thetransmission system of claim 28, comprising: a buffer for receiving saidplurality of sets of samples; an integral transform module forsubjecting said plurality of sets of samples in said buffer to anintegral transform to generate signals to be transmitted in an integraltransformed format; and sample allocation circuitry for selectivelyarranging at least one set of generally non-zero samples to betransmitted in a respective position of said buffer.
 35. The transmitterterminal of claim 34, wherein allocating circuitry is configured forallocating at least a single set of generally non-zero samples in asingle, respective set of positions of said buffer, said set allocationbeing indicative of said transmitter terminal.
 36. The transmitterterminal of claim 33, comprising an RF module operating in themillimetre-wave range.
 37. The transmitter terminal of claim 36, whereinsaid RF module operates in the range of 60 GHz.
 38. A receiver terminalfor the transmission system of claim 28, comprising: a receiver forreceiving samples transmitted in said integral-transformed format; abuffer for receiving said plurality of sets of samples; a complementaryintegral transform module for subjecting said sets of samples in saidbuffer to a complementary integral transform and reconstructingtherefrom said at least one set of generally non-zero samples; andsample allocation circuitry for selectively arranging at least one setof generally non-zero samples in a respective position of said buffer.39. The receiver terminal of claim 38, wherein said allocating circuitryis configured for allocating at least a single set of generally non-zerosamples in a single, respective set of positions of said buffer, saidset allocation being indicative of the transmitter.
 40. The receiverterminal of claim 38, comprising a receiver operating in themillimetre-wave range.
 41. The receiver terminal of claim 40, whereinsaid receiver operates in the range of 60 GHz.
 42. A computer programproduct directly loadable in the internal memory of a computer andincluding software code portions performing the method of claim 23,where said product is capable of running on a computer.
 43. A computerprogram product directly loadable in the internal memory of a computerand including software code portions for implementing the transmitterterminal of claim 34, where said product is capable of running on acomputer.
 44. A computer program product directly loadable in theinternal memory of a computer and including software code portions forimplementing the receiver terminal of claim 38, where said product iscapable of running on a computer.